To search that a given asset is shared amongst sites we use asset:sites
tag
<asset:load name="loadReferences" type="[c]" objectid="[cid]"/>
<asset:sites list="sharedSites" name="loadReferences"/>
<ics:if condition='<%=null!=ics.GetList("sharedSites") && ics.GetList("sharedSites").hasData()%>'>
<ics:then>
<ics:listloop listname="sharedSites">
<ics:listget fieldname="id" listname="sharedSites"/> :
<ics:listget fieldname="name" listname="sharedSites"/> :
<ics:listget fieldname="description" listname="sharedSites"/><br>
</ics:listloop>
</ics:then>
</ics:if>